This invention relates to a filament for irradiating a living body, comprising a core of material capable of irradiating radioactive radiation after activation, the core being clad in a casing of protective material, wherein the materials forming the core and casing differ from one another.
The invention also relates to a method for producing a filament for irradiating a living body.
Endoluminal brachytherapy, and more particularly percutaneous transluminal brachytherapy, currently face difficulties for handling the radioactive material, either on a therapeutical viewpoint or on a manufacturing viewpoint. As a matter of fact, it is quite frequent that the structure embodying the radioactive material is bulky and lacks flexibility, whereby the material is difficult to operate through tortuous vessel configurations or narrow passages thereof; this may cause damage or even destruction of the radioactive structure together with the resulting risk of harmful influence on the organism. Furthermore, the radioactive material may enter into direct contact with the vessel walls, which greatly amplifies the risk of unwanted damage to the vessel. And when the radioactive material is merely coated or covered by an outer material, the coating or cover may help protecting the vessel wall from direct contact with the radioactive source, but there is still a substantial danger of having the radioactive material or particles thereof entering into unwanted contact with the vessel wall in case of deterioration of the coating or cover or because the coating or cover still have uncontrolled pores through which the radioactive material may cause damage to the vessel.
For example, the document WO 93/04735 describes an apparatus for the treatment of an artery, comprising a radioactive dose and means operatively connected to such a dose to bring it into a selected region of an artery. In one embodiment, the apparatus comprises a wire wound sheath removably positioned over a windowed housing made of a wire winding containing a radioactive dose, whereby relative motion between the sheath and housing permits moving the windowed housing in and out of the sheath to expose the radioactive dose in some place of an artery. In another embodiment the apparatus comprises a motion wire having a radioactive dose affixed at its distal end and a retractable sheath formed of a helically wound member positioned over the motion wire and radioactive configuration to provide a measure of shielding to the radioactive dose during insertion and removal of the system into an artery, whereby the sheath may be retracted to expose the radioactive dose at a selected place in the artery. A further embodiment comprises a shaft portion having at its distal end a canister containing a radioactive dose and provided with a remotely actuated window which can be manipulated to expose the radioactive dose in an injured area of an artery. In a still further embodiment, a plurality of radioactive dose means are encased in a heat shrinkable polymer catheter tip having spacers made of a meltable material to provide encapsulation of the radioactive dose means, which provides flexibility of the apparatus but not longitudinal homogeneity of the radioactive source. In a balloon configuration of the apparatus, radioactive elements are affixed to the outer surface of an angioplasty balloon. In a stent arrangement of the apparatus, the radioactive element may be associated with an expandable stent and it is the radioactive means that may be included in the stent as a cladding, a coating, or an additive within the basic stent material, or an attachment by other means to the stent.
As a further example of the aforesaid drawbacks, U.S. Pat. No. 5,059,166 describes an intra-arterial stent with the capability to inhibit intimal hyperplasia by means of radioactive radiation. The document refers to a radioisotope integral to an arterial stent which can irradiate the tissue in close proximity to the implantation site of the stent. In one embodiment, a helical coil spring stent is fabricated from a pure metal or alloy which has been activated so that it has become radioactive, i.e., it is a radioisotope; the radioisotope used for this purpose may be an alpha, beta, or gamma emitter, a beta emitter such as Vanadium 48 being preferred because of its short travel in human tissue and 16 days half-life and only 8% of emitted energy from gamma radiation. In another configuration, the stent spring wire is made from a metal such as steel into which is alloyed an element that can be made into a radioisotope, for example Phosphorus 32 which is a 14.3 day half-life beta emitter. In a further configuration, the stent wire is made from a radioisotope core material with an outer covering that has the attributes that are desirable for being a coil spring. In a variant, the stent wire is made of a radioisotope coating plated onto a spring material core. Still a further embodiment shows a more complex configuration in which a core of some material suited for stents is plated with a radioisotope coating which is in turn coated with an anti-thrombogenic coating such as carbon.
Within the frame of a centering configuration aimed at uniformly applying a radioactive radiation to a vessel wall, the document EP 0633041 A1 outlines the use of a radioactive emitter in the form of a filament of small diameter, which may be coiled. Filament technology has the advantage of a dense concentration of the radioactive dose in a small volume of the source allowing a reduced diameter and a better maneuverability in narrow and/or tortuous vessels. In one embodiment, the filament may be made of 89 Yttrium heat elaborated under vacuum to a diameter equal to or less than 0.2 mm.
In the environment of a medical appliance for the treatment of body vessels by ionizing radiation described in EP 0 686 342 A1, published Dec. 13, 1995, the filament technology is enhanced by having a filament, which may be in the form of a coil, coated by a neutral material such as Titanium.
Clad composite filaments are generally shown in WO 94/16646 and WO 95/30384.
All documents cited herein, including the foregoing, are incorporated herein by reference in their entireties for all purposes.
It is an object of this invention to improve the conditions of use in a patient as well as those of handling the sources used for irradiating a living body and more particularly those sources used for endoluminal or percutaneous transluminal brachytherapy. It is a further object of the invention to improve such conditions by means of a filament which is highly safe.
Still a further object of the invention is a method for manufacturing a filament for irradiating a living body which is fully controllable, devoid of hazardous technological operations with radioactive substances, and which results in a product which practically eliminates the risk of having radioactive core materials or particles thereof entering into unwanted contact with a living body.